linux-kernel - [PATCH v2] mm: ksm: Consider the number of ksm_mm_slot in the general

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Message-Id: <20240620043914.249768-1-sfoon.kim@samsung.com>
Date: Thu, 20 Jun 2024 13:39:14 +0900
From: Sung-hun Kim <sfoon.kim@...sung.com>
To: akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: sungguk.na@...sung.com, sw0312.kim@...sung.com, sebuns@...il.com,
	Sung-hun Kim <sfoon.kim@...sung.com>
Subject: [PATCH v2] mm: ksm: Consider the number of ksm_mm_slot in the
 general_profit calculation

The current version of KSM does not take into account the number of
used ksm_mm_slot. Therefore, when users want to obtain profits of
KSM, KSM omits the memory used for allocating ksm_mm_slots.

This patch introduces a new variable to keep track of the number of
allocated ksm_mm_slots. By doing so, KSM will be able to provide a
more accurate number of the gains made.

Signed-off-by: Sung-hun Kim <sfoon.kim@...sung.com>
---
Changelog in V2:
- Add an MMF_VM_MERGEABLE flag check in ksm_process_profit for
untracked processes
---
 mm/ksm.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 34c4820e0d3d..c8ced991ccda 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -267,6 +267,9 @@ static unsigned long ksm_pages_unshared;
 /* The number of rmap_items in use: to calculate pages_volatile */
 static unsigned long ksm_rmap_items;
 
+/* The number of ksm_mm_slot in use */
+static atomic_long_t ksm_mm_slots = ATOMIC_LONG_INIT(0);
+
 /* The number of stable_node chains */
 static unsigned long ksm_stable_node_chains;
 
@@ -1245,6 +1248,7 @@ static int unmerge_and_remove_all_rmap_items(void)
 			spin_unlock(&ksm_mmlist_lock);
 
 			mm_slot_free(mm_slot_cache, mm_slot);
+			atomic_long_dec(&ksm_mm_slots);
 			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 			clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
 			mmdrop(mm);
@@ -2717,6 +2721,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 		spin_unlock(&ksm_mmlist_lock);
 
 		mm_slot_free(mm_slot_cache, mm_slot);
+		atomic_long_dec(&ksm_mm_slots);
 		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
 		mmap_read_unlock(mm);
@@ -3000,6 +3005,7 @@ int __ksm_enter(struct mm_struct *mm)
 		list_add_tail(&slot->mm_node, &ksm_scan.mm_slot->slot.mm_node);
 	spin_unlock(&ksm_mmlist_lock);
 
+	atomic_long_inc(&ksm_mm_slots);
 	set_bit(MMF_VM_MERGEABLE, &mm->flags);
 	mmgrab(mm);
 
@@ -3042,6 +3048,7 @@ void __ksm_exit(struct mm_struct *mm)
 
 	if (easy_to_free) {
 		mm_slot_free(mm_slot_cache, mm_slot);
+		atomic_long_dec(&ksm_mm_slots);
 		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
 		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 		mmdrop(mm);
@@ -3374,7 +3381,8 @@ static void wait_while_offlining(void)
 long ksm_process_profit(struct mm_struct *mm)
 {
 	return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * PAGE_SIZE -
-		mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
+		mm->ksm_rmap_items * sizeof(struct ksm_rmap_item) -
+		(test_bit(MMF_VM_MERGEABLE, &mm->flags) ? sizeof(struct ksm_mm_slot) : 0);
 }
 #endif /* CONFIG_PROC_FS */
 
@@ -3672,7 +3680,8 @@ static ssize_t general_profit_show(struct kobject *kobj,
 	long general_profit;
 
 	general_profit = (ksm_pages_sharing + atomic_long_read(&ksm_zero_pages)) * PAGE_SIZE -
-				ksm_rmap_items * sizeof(struct ksm_rmap_item);
+				ksm_rmap_items * sizeof(struct ksm_rmap_item) -
+				atomic_long_read(&ksm_mm_slots) * sizeof(struct ksm_mm_slot);
 
 	return sysfs_emit(buf, "%ld\n", general_profit);
 }
-- 
2.25.1